Couple reasons I think many do better on Gary Senkos. They are heavier (more salt which is ballast) and they are softer. Both reasons why they are not durable.
Home injectors have found a salt substitute that resuls in a VERY durable stick that weighs the same, sinks the same, wiggles the same, and are as soft as a Senko. I guess the big companies wont use it because they would sell way less baits if the dont fall apart.